A typical color video monitor may consume as much as 50 to 80 percent of the total electrical energy consumed by a personal computer (PC). A video monitor dissipates this energy as visible light emissions from screen phosphors, thermal waste, electromagnetic radiation, high-energy radiation and acoustic energy. Only the phosphor emissions are normally considered useful and then only when actively being watched by an observer. The radiation emissions have been a hotly debated source of concern regarding possible health risks from long-term exposure. Manufacturers incur considerable extra expense to reduce radiation emissions from video monitors. Some people are annoyed by the acoustic emissions produced by some monitors. Thermal losses from video monitors contribute an additional load on air conditioning equipment. The energy efficiency of video monitors has historically improved mostly as a result of advances in the electronic circuit components such as the increased use of integrated circuit (IC) devices. Cathode ray tube (CRT) technology has improved rather little in terms of energy efficiency.
The number of PC's in regular use in growing rapidly and has reached a point where they have become major consumers of electric power. The United States Environmental Protection Agency has issued power efficiency targets for computer manufacturers to design for in new systems. Low-voltage IC's use less energy, and microprocessor power management techniques allow a computer to reduce energy consumption when idling. Until a suitable replacement for the CRT or a more efficient CRT is developed it will be difficult to substantially improve personal computer energy efficiency.
What is needed is a way to shut down high-energy-consuming circuits in the video monitor when the computer determines that the display may be of no interest to anyone. This might be determined by a period of inactivity on input devices such a modem, mouse and keyboard. Many computers and video terminals use such a technique to activate a screen blanking circuit or a program that displays moving images (or no image) to avoid burning the screen phosphors. Activating an input device such as pressing a key or moving a mouse causes the previous screen image to be restored. This technique can be extended to reduce video monitor power consumption by signalling the microcontroller found in many recent design monitors, or an add-on device for "dumb" monitors, to shut down or restore some or all of the monitor's electrical power circuits. One key to accomplishing this end is a means of signalling a monitor to shut down to some selected level without adding to the signals presently provided to a monitor.